Stabilized optical gimbal assembly

ABSTRACT

A two axis optical FLIR gimbal assembly for azimuth and elevation supporting an assembly of optical elements including five folding mirrors, one of which is a Mangin mirror, and six lenses which implement a wide stabilized field of regard and provide a magnification of the incident image. The gimbal assembly, moreover, includes a yoke structure which is driven about an azimuth axis and supports a stable body member which is independently driven about an elevation axis. An independently driven turret is also rotatable about the azimuth axis and shields the gimbal assembly from external forces such as an air stream passing over the fuselage of an aircraft.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to the following application which isassigned to the assignee of this invention:

"Optically Multiplexed Dual Line of Sight FLIR System", U.S. Ser. No.07/754,777 (W.E. 57,082), filed on Sep. 4, 1991.

BACKGROUND OF THE INVENTION

This invention relates generally to optical imaging systems located on aplatform, for example an aircraft, and more particularly to a stabilizedoptical gimbal assembly used in connection with a forward lookinginfrared target acquisition and tracking apparatus utilized in weaponsdelivery systems.

Sophisticated optical imaging systems normally require some sort ofsealed enclosure, particularly when exposed to the elements. When theoptical imaging system is mounted on an aircraft, particularly highperformance military aircraft, it is extremely important to keep thesize of the sealed enclosure as small as possible in order to minimizethe aerodynamic effects on the aircraft. The enclosure inherentlyincludes some type of window through which the internal optical systemcan view the outside world. In order to increase system efficiency, itis necessary to make this window as large as possible in order tomaximize the amount of light that can be collected for imaging and isreferred to as the "clear aperture" and is one of the most importantparameters in determining system performance. Accordingly, one of themajor problems in any system design is to maximize the clear aperturesize in the smallest possible enclosure. In other words, one attempts tomaximize the ratio of clear aperture diameter to enclosure diameter orsome other maximum dimension.

The optics, moreover, are normally mounted on a stabilized gimballocated just inside the window. The gimbal directs the line of sight ofthe optical system in azimuth and/or elevation relative to aircraftcoordinates, thereby generating what is referred to as the "field ofregard" of the system. The larger the field of regard, the better. Wherethe system is used to track targets for a weapons system, the gimbalmust also be well stabilized so that any jitter in the image displayedto the operator is eliminated. All of this requires motors, resolvers,gyros, bearings, well known to those skilled in the art which complicatethe problem of maximizing the ratio of clear aperture to enclosurediameter.

Gimbal enclosures are typically referred to as shrouds or turrets. As aresult, one attempts to maximize the ratio of the clear aperturediameter as measured at the outside surface of the windows to the turretoutside diameter. Many different optical gimbal schemes have beenpreviously designed in an effort to maximize the ratio of clear aperturediameter to turret outside diameter but have been known to achieve aratio only on the order of 0.50.

SUMMARY

Accordingly, it is the primary object of the present invention toprovide an improvement in stabilized gimbal mounted optical imagesystems.

It is another object of the invention to provide an improvement instabilized gimbal optical systems enclosed in a turret.

And it is yet another object of the invention to provide an improvementin stabilized gimbal optical systems for maximizing the ratio of theclear aperture diameter to the turret outside diameter.

Briefly, the foregoing and other objects are achieved by a two axisgimbal assembly for azimuth and elevation which supports an assembly ofoptical elements including five folding mirrors, one of which is aMangin mirror, and six lenses which implement a wide stabilized field ofregard and provide a magnification of the incident image. The gimbalassembly, moreover, includes a yoke structure which is driven about anazimuth axis and supports a stable body member which is independentlydriven about an elevation axis. An independently driven turret is alsorotatable about the azimuth axis and shields the gimbal assembly fromexternal forces such as an air stream passing over the fuselage of anaircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the invention will be more readilyunderstood when considered in light of the accompanying drawingswherein:

FIG. 1 is a perspective view of an aircraft which acts as a platform forthe subject invention;

FIG. 2 is an exploded perspective view generally illustrative of theinvention;

FIG. 3 is a mechanical schematic diagram generally illustrative of thesubject invention and being in the form of a central vertical crosssection thereof;

FIG. 4 is a perspective view partially cut away of the optical elementsincluded in a preferred embodiment of the invention;

FIG. 5 is a side planar view of a central vertical cross section of theembodiment shown in FIG. 4;

FIG. 6 is an enlarged sectional view of FIG. 5 taken along the lines6--6 thereof; and

FIG. 7 is a perspective view further illustrative of the preferredembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein like reference numerals refer tolike components throughout, reference is first made to FIG. 1 whereinthere is shown an aircraft 10 which in addition to having a radar systemgenerally denoted by reference numeral 12 located in the nose portion 14thereof, also includes a pair of forward looking infrared (FLIR) turrets16 and 18 which are used in conjunction with the radar system 12 toprovide both a navigation (pilotage) and a weapons delivery guidance(targeting) function or mode in a single integrated system which isshown and described in the above-referenced related applicationentitled, "Optically Multiplexed Dual Line of Sight FLIR System", U.S.Ser. No. 07/745,777 and which is incorporated herein by reference.

One of the turrets 18 which is used for targeting, for example, includesan optical gimbal system, the details of which are shown in FIGS. 2through 7. More particularly, and as shown in FIG. 2, the turret 18 usedfor targeting is comprised of a stabilized gimbal assembly 20 which actsas a mount for a compact lens and mirror configuration, to be explainedhereinafter, located in a mechanical turret structure 22 and whichincludes a turret housing 24 and a front window 26 which is mounted on aframe 28 fastened to the housing 24.

The housing 24 defines a portion of a sphere while the front window 26and frame 28 defines another portion of the same sphere. Moreover, thefront window 26 is curvilinear and is of a size so as to provide a clearaperture C.A. of a predetermined diameter dimension, for example, asshown in FIG. 5, relative to the diameter of the housing or turret 24such that the ratio of the clear aperture diameter dimension to theturret diameter dimension is relatively large, e.g. 0.69. The frontwindow 26 as configured in FIG. 2 provides a field of regard along anelevation axis 40 (FIG. 4) of, for example, 10° down and 70° up relativeto a 0° elevation direction.

Prior to discussing the details of the gimbal assembly 20, referencewill first be made to FIG. 3 which broadly sets forth the concept of agimbal assembly 20, not only being shielded from the external forces ofthe air stream by the turret 22 but also being independently rotatabletherein. As shown, the turret 18 is rotatable about an azimuth axis 30on a set of bearings 32 and 33, and by a turret drive assembly, notshown. The gimbal assembly 20 is comprised of two major components, ayoke 34 which is mounted on another set of bearings 36 and 37, and whichis independently rotatable about the azimuth axis 30, and a structure 38which is referred to as a stable body and which is mounted on the yoke34 and being independently rotatable about an elevation axis 40 by meansof bearings 42 and 44.

Referring now to FIG. 4, shown thereat is the three dimensionalrelationship of the optics included in the subject invention and whichis further disclosed in FIGS. 5 and 6. Collectively, these figuresillustrate a spherically shaped window 26 (FIG. 2) behind which ismounted the stable body member 38 and which is rotatable around theelevation axis 40 while being held in place by the yoke 34 The yoke 34additionally includes a pair of upper semi-circular support ringsegments 46, 48 and a pair of lower support ring segments 47, 49 (FIG.7) which support and hold the bearings 42 and 44 as well as thecomponents of a pair of drive motor and resolver assemblies 50 and 51.

The physical construction of the yoke structure 34 is shown in FIG. 7and will be referred to subsequently. The stable body member 38comprises a semi-cylindrical structure to which is secured a generallycircular front lens 52 comprised of material which readily passesinfrared energy and which is located immediately behind the window 26.Also mounted thereon is an angulated mirror 54 (FIG. 6) having anaperture 56 at the center. A second mirror 58 is also mounted on thestable body and is located to the side and adjacent the mounting ring48. The mirror 58 comprises a well known Mangin mirror and reflectsenergy through the aperture 56 to a second relatively smaller lens 60which is also mounted on the stable body 38 and located behind themirror 54 and orthogonal to the elevation axis 40. The two lenses 52 and60 and the two mirrors 54 and 58 being mounted solidly on the stablebody 38 are adapted to rotate about the axis 40 elevation.

The stable body 38, moreover, is designed to have a peripheral slot 62which accommodates an upwardly extending support structure 64 (FIG. 7)on the yoke 34 which supports a third mirror element 66, a pair oflenses 68 and 70, fourth and fifth mirrors 72 and 74, and a pair ofoutput lenses 76 and 78 as best shown in FIG. 4. These elements rotateonly in azimuth and not in elevation.

The three mirrors 66, 72 and 74 are comprised of generally flat facedreflectors which are tilted and angulated downwardly and operate incombination with the mirrors 54 and 58 to fold the received opticalenergy in an extremely compact gimbal package. Such an arrangementprovides a magnification on the order of x11 of the incident image onthe front lens 52.

Referring now briefly to FIG. 7, a support structure 80 including thelower semi-circular support members 47 and 49 to which the uppersemi-circular support rings 46 and 48 (FIG. 4) attach is shown furtherincluding an upwardly extending mirror support member 64 for member 66located adjacent the support ring 47 and on which is secured a generallyflat apertured plate member 83 which supports and holds the lens 68. Thelens 70 (FIG. 4) is located beneath the lens 68 where it directs opticalenergy to the mirror 72 which is shown from its rear side and beingsecured to a support member 84. The fifth mirror 74 and the two outputlenses 76 and 78 are not shown but are located within a circular base86.

Below the base 86 are several circular members 88 and 90 which operateas balance weights while the member 92 constitutes a shaft element for amotor rotor 94 which is adapted to rotate the yoke 34 around the azimuthaxis 30. Behind the mirror and lens support structure 84 is shown aturret bumper stop member 96 which is adapted to restrict rotation ofthe yoke 34 around the azimuth axis 30 relative to the turret rotation.

Thus what has been shown and described is an imaging gimbal assemblywhich is adapted to have a ratio of clear aperture diameter to turretdiameter on the order of 0.69 with field of regard in elevation from 10°down and 70° up relative to a 0° elevation (normal forward) direction,while the azimuth field of view can be made 360°, when desirable.

While the subject invention is particularly applicable to being mountedon an aircraft, it should be noted that the invention is applicable toany operational environment which requires a stabilized optical gimbalhaving the largest possible clear aperture diameter for a given turretdiameter. It can also be used for systems with any optical wavelengthand may be utilized on ground vehicles, ships and even stationaryapplications, both military and non-military.

Having thus shown and described what is at present to be the preferredembodiment of the invention, it should be noted that the same has beenmade by way of illustration and not limitation. Accordingly, allmodifications, alterations and changes coming within the spirit andscope of the invention are herein meant to be included.

What is claimed is:
 1. A stabilized optical gimbal assembly,comprising;turret means including a relatively large aperture rotatableabout a first axis; a yoke located within the turret means and beingindependently rotatable about said first axis; a stable body membermounted on and supported by the yoke and being independently rotatableabout a second axis orthogonal to said first axis; a first lens mountedacross a forward portion of the stable body member and being orientedtoward a predetermined line of sight; a first mirror having a centralaperture mounted on the stable body member behind the front lens andangulated relative thereto; a second mirror mounted on said stable bodymember to one side thereof and adjacent said first mirror for receivingoptical energy reflected therefrom and directing said optical energythrough said central aperture; a second lens mounted on said stable bodymember behind said first mirror and aligned with said central aperture;a third mirror mounted on said yoke in alignment with said second lensand angulated relative thereto for receiving optical energy from saidsecond lens and directing said energy through an opening in a rearportion of the stable body; a first lens assembly located in saidopening for receiving optical energy from said third mirror; a fourthmirror angularly mounted on said yoke behind said stable body member forreceiving optical energy from said first lens assembly; a fifth mirrorangularly mounted on said yoke beneath said stable body member forreceiving optical energy from said fourth mirror; and a second lenssystem mounted on said yoke for receiving optical energy from said fifthmirror and directing optical energy out of the gimbal assembly.
 2. Thegimbal assembly as defined by claim 1 wherein said second mirrorcomprises a Mangin mirror.
 3. The gimbal assembly as defined by claim 2and additionally including a support structure on said yoke andextending into said opening of the stable body member for supportingsaid third mirror, said at least one third lens, and said fourth andfifth mirrors.
 4. The gimbal assembly as defined by claim 3 wherein saidfirst axis comprises an azimuth axis and wherein said second axiscomprises an elevation axis.
 5. The gimbal assembly as defined by claim4 wherein said yoke comprises an upright member whereby said thirdmirror, said first lens assembly, and said fourth and fifth mirrorsrotate only about said azimuth axis while said first and second lensesand said first and second mirrors rotate about said elevation axis. 6.The gimbal assembly as defined by claim 5 wherein said stable bodymember comprises a cylindrical type structure mounted on and held inplace on said yoke by opposing pairs of upper and lower semi-circularsupport ring segments.
 7. The gimbal assembly as defined by claim 6wherein said pairs of upper and lower support ring segments additionallysupport drive motor means for rotating said stable body member.
 8. Thegimbal assembly as defined by claim 7 and additionally including drivemotor means for rotating said yoke.
 9. The gimbal assembly as defined byclaim 8 wherein said first lens assembly comprises a pair of lenses. 10.The gimbal assembly as defined by claim 9 wherein said second lensassembly comprises a pair of lenses.
 11. The gimbal assembly as definedby claim 1 wherein said turret means includes a housing and a frontwindow attached to said housing, and wherein said first lens is locateddirectly behind said window.
 12. The gimbal assembly as defined by claim11 and additionally including a frame for attaching said window to saidhousing.
 13. The gimbal assembly as defined by claim 12 wherein saidhousing defines a portion of a sphere and said front window and framedefine another portion of a sphere.
 14. The gimbal assembly as definedby claim 13 wherein said first axis comprises an azimuth axis and saidsecond axis comprises an elevation axis and said front window includes alength dimension along said azimuth axis which is greater than a widthdimension along said elevation axis.
 15. The gimbal assembly as definedby claim 14 wherein said front window is curvilinear and includes apredetermined clear aperture diameter dimension relative to a diameterdimension of said housing.